1. Field of the Invention
The present invention relates to a display panel for modulating an incident light to form an optical image by controlling the scattering due to the liquid crystal and a projection display system which uses the display panel as a light valve and amplifies an image displayed on the display panel.
2. Description of the Prior Art
A display device employing a liquid crystal display panel has been researched and developed widely because of its compact size and its light weight. Recently, pocket television sets employing a twisted nematic (TN) mode liquid crystal display panel have been used practically. Furthermore, projection television systems, viewfinders and the like using a liquid crystal display panel as a light valve have also been used practically.
However, a TN mode liquid crystal display panel which uses the chirality of liquid crystals has disadvantages such as low brightness of display because two polarization plates are needed for light modulation. Furthermore, fabrication steps are complex. For example, rubbing is needed in order to align liquid crystal molecules. Recently, display panels using liquid crystal/resin composite have attracted attention because they need no polarizing plates and no rubbing step on fabrication. U.S. Pat. No. 4,435,047 discloses a display panel using liquid crystal/resin composite, and U.S. Pat. No. 4,613,207 discloses a projection display system which uses a display panel including a liquid crystal/resin composite as a light valve.
However, there remains problems before such a display panel of liquid crystal/resin composite can be used practically. One of the problems is that light reflected from a pixel propagates or leaks to adjacent pixels. This makes the contour of a pixel unclear. This problem is more important for a black and white image displayed with very small pixels. That is, a pixel of black or white becomes gray due to light scattered from adjacent pixels.
In a fabrication technique disclosed in Japanese Patent Laid-Open Publication 4-84121/1992, black walls made of a saturated hydrocarbon are formed between pixel electrodes on the source lines for applying a voltage to the pixels. Light scattered from a pixel is absorbed by the black walls to prevent the leakage of light to adjacent pixels. However, the thickness of the liquid crystal/resin composite must be 10 .mu.m or more, and this means that the height of the walls have to be at least as high as about 10 .mu.m. It may be possible to form such a wall by using a print technique. However, it is impossible to form such a wall for a display panel with one million pixels or more in an effective display area of a size of three inches or the like. In such a display panel, the pixel size is about 50 .mu.m and the distance between them is about 5 .mu.m. Therefore, the wall has a width of about 5 .mu.m and a height of about 10 .mu.m. The width of 5 .mu.m cannot be produced with a pattern print technique. Such a small width may be realized with a deposition technique such as sputtering, but the height of about 10 .mu.m cannot be realized by the technique. Furthermore, is also a problem that the wall is made of a hydrocarbon material because a hydrocarbon material may have a bad insulating property. Because the wall is formed between a pixel electrode and a counterelectrode, the insulation between the two electrodes may be deteriorated. Furthermore, the hydrocarbon may react with a component of the liquid crystal or deteriorate the liquid crystal.